At present, the power taken by elevators from the electric supply netork varies greatly. The power required is at a maximum during ascent of a fully loaded elevator car, and this maximum power determines the design of the electrical equipment and interface. During descent of the elevator car, the car can be braked electrically by feeding electric energy back into the network. Often, however, all of the kinetic and potential energy of the elevator car is converted into waste heat in suitable braking devices.